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  1. #1

    Confused

    Greetings:
    I just purchased an anemometer so I can calculate flow into returns and out supplies to see if there are any serious duct leaks. Once I know the average velocity through the louvers, I need to plug in an area for the calculation.

    Seems to me there is a relatively constant factor, (perhaps mfgr. dependant) somewhere in the vicinity of .75-.81 to use, but I am not sure of:

    1. what factor to use?
    2. where to measure the louver: outside edges of frame, or inside where the louvers begin?

    Thanks.

  2. #2
    Join Date
    Nov 2004
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    2,927
    1.those numbers sound good...yes the manufacturer will be able to tell you the exact number.

    2.where the louvers begin(but I am guessing as to your meaning)

    try this measure the free area ,say 20 @1 inch x 5 inch areas in one grill...that would be 100 square inches

    there is an online catalog that should have them listed,if you know brand ,size ,item number

  3. #3
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    You'll get close,if you are diligent,but there are better ways to do this.

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    self edit
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Aug 2002
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    Originally posted by Carnak
    self edit


    Interesting??

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
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    6,296

    Mfg Info

    Originally posted by beachwalker
    I just purchased an anemometer so I can calculate flow into returns and out supplies to see if there are any serious duct leaks. Once I know the average velocity through the louvers, I need to plug in an area for the calculation.
    All the manufacturers have on-line catalogs.
    See Ak

    For example,
    http://www.titus-hvac.com/ecatalog/
    http://www.metalaire.com/products_full_page.htm
    http://www.hartandcooley.com/grd/all_grd.htm

    __ Louvers, ?
    You mean Return Air registers and S.A. diffusers?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7

    Measuring Air Velocities Thru Louvers

    I would not recommend maesuring the air flow thru louvers. The way that the air flow enters or leaves a louver is hard to determine with a wind vane anemometer due to the erratic velocities. A hot wire anemometer would be better but you would need to take several readings to get a good average and record readings in places around the louvers that you may not realize.
    Both anemometers would be fine for diffuser or grille measurements as long as you follow the instruments instructions and get a true average.
    Most of the prominant manufactures list the "K"Factors for their products in the catalog or you can get some of them on the web.

    Remember to apply the correction factors for altitude if you are measureing air flows above 2000 feet above sea level. Some instruments require a temperature correction factor as well.

  8. #8
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    plastic grills have much less free space!
    about 66% by my rough measuring, I changed back to metal!

  9. #9
    Join Date
    Feb 2004
    Location
    Central Kansas
    Posts
    1,145

    How about those decorative wooden grills?

    Nice to look at but I bet the net free area is less than 50%. The ones I have seen had no label or data regarding net free area. Greg

  10. #10

    Smile

    As usual, this forum provides fast and useful answers. To clear up the louver question, I should have more properly described them as return and supply registers.

    And thanks for the mfgr links... I have a mix of what looks like Hart & Cooley and a few replacements purchased at "The Depot" as the originals showed some rust.

    When we had our wood floor re-finished last year, we also had about six oak louvers installed and they look to be much more restrictive (less free area) than the metal. I guess the best thing to do is measure them directly.

    When I measured the airflow from the grills I was intending to take multiple measurements across the face and use the average to account for variations.

    Is there a proceedure for "balancing" the airflow as far as cfm's per room? Is it proportional to loads calculated by room in the manual J calculations, or it that over the edge a bit?

    Thanks again to everyone.

  11. #11
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Yes ,proprotional to the Man. J load for each room,based on total system cfm.


    You may need to lose the wood grilles.

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